A Prototype Of An Adaptive, Multi-Feedstock, Anaerobic Biomass Digester For Biogas Production

ABSTRACT

In this work, the production of biogas from local biomass has been studied through the design, construction and operation of a single-stage, multi-feedstock anaerobic digester, with the aim of providing the scientific and technological bases for the mass assembly and deployment of modular and scalable bio-digester system, using components obtainable in Ghana. A horizontal cylindrical plastic tank (1 m3) with torispherical ends has been developed into an air-tight (sealed) anaerobic digester. The factors considered in the design and operation include the type of organic material as feedstock and digester portability. The assembled digester was operated as a bench system for a cycle of 24 days under mesophilic temperature conditions. The maximum and minimum temperatures recorded during the operation of the digester were 38.5 oC and 32.4 oC respectively. The average operating temperature was 36.1 ± 1.5 oC. A slurry of fresh cow dung with calorific value of 26.45 MJ kg-1 was used as substrate for the study. The final composition of the biogas produced was 60.2 % CH4 and 39.7 % CO2, with the highest daily gas production of 0.474 m3, which was measured on the 18th day. A motorized stirrer and a thermostatically operated heat exchanger system were used to ensure there were no temperature and concentration gradients during the operation of the digester. The performance of the digester is deemed satisfactory and confirms that this pilot-scale prototype is a valid proof of concept and can therefore be used as the basis for the design and assembly of production-scale digester systems.